It will be appreciated that certain aluminum alloys have been found highly acceptable for use in constructing the frictionally engaging piston and cylinder members of compressors or engines. In those instances where weight, heat conduction, economics and mass production are important considerations, it is advantageous to employ a pressure and die-casting process in fabricating the aluminum alloy pistons and cylinders. However, the use of only aluminum base material for both of the friction members, which are exposed to enormous stresses and experience high sliding speeds, generally results in the rapid wear of materials and deterioration during the operation of the piston-cylinder devices. For this reason it is advisable to separate the eutectic or hypereutectic aluminum alloy cylinder member from the eutectic aluminum alloy piston member by coating at least one of the two contact surfaces.
Previously, coating processes of this type were described in the Motor-Technical Journal (MTZ) No. 2/1973 in article entitled "Unsheathed Aluminum Cylinders for Combustion Motors." Further, another specific process of this type was also published in the MTZ No. 2/1974 in an article entitled "Alusil-Cylinder and Ferrocoat-Pistons for the Porsche-Motor 911." When using hypereutectic alloys for the cylinder material, it is common practice to coat the aluminum friction piston member, in order to achieve the separation between the two base metal members. This separation is accomplished by using a coating of iron, chromium, nickel or by using so-called glide varnishes with MOS 2 or graphitic constituents.
Another known method is to coat the inside of the cylinder in a similar manner instead of the piston which is considerably more costly and difficult to achieve.
Presently, it is also common practice to chemically etch the light metal cylinders which are cast from the aluminum alloys, in order to expose the silicon constituents for the purpose of forming a resistant surface.
It will be appreciated that all of the previously known coating processes are relatively costly to carry out and manifestly difficult from a process engineering standpoint.